bts: Move struct gprs_rlcmac_bts and other structs into a bts.h

Begin to make the BTS a real C++ object with real responsibilities.
The biggest issue will be the pcu_vty.c that might not like C++
at all.
diff --git a/tests/emu/pcu_emu.cpp b/tests/emu/pcu_emu.cpp
index b68b856..4b58a8b 100644
--- a/tests/emu/pcu_emu.cpp
+++ b/tests/emu/pcu_emu.cpp
@@ -29,6 +29,7 @@
 
 #include <gprs_bssgp_pcu.h>
 #include <gprs_rlcmac.h>
+#include <bts.h>
 
 #include <stdlib.h>
 #include <sys/types.h>